CHARLESTON, South Carolina — Bernie Sanders shined in Sunday night’s Democratic debate here, at times overpowering Hillary Clinton in a format she typically controls. With polls showing Clinton on the ropes in Iowa and New Hampshire, Sanders’ strong performance may have further imperiled Clinton’s once-inevitable path to her party’s presidential nomination.

Touting his surging poll numbers in the two key early states, Sanders was prepared and in command throughout the two-hour debate sponsored by NBC News and YouTube. In previous appearances, Clinton has easily dominated the stage. But turning in his strongest debate performance yet, Sanders drove the conversation – brushing aside her attacks as he doggedly returned to his core message of political revolution.

In the long arc of a primary campaign that began with warm relations between the two top candidates only to turn acrimonious over side issues, Sunday night was the first time voters saw the core divide between Clinton and Sanders.

They clashed over their approach to governing �— revolution or evolution — in a way that's been hinted at since the day each got into the race but that was somewhat obscured until now.

The debate came at a critical moment in the campaign, just 14 days before the Iowa caucuses, where a surge in enthusiasm for Sanders, especially among younger voters, has suddenly made Iowa’s contest a dead heat.

Clinton’s campaign has struggled to respond to the passion-gap, and Clinton emphasized her pragmatism Sunday night.

While Sanders urged his audience to “think big,” Clinton reminded them that “details matter.” While Clinton used her opening remarks to say she was “prepared and ready,” Sanders used his to make a passionate case for the “rigged economy.” Clinton again aligned herself with President Obama, saying she would continue his legacy and suggesting Sanders hadn’t been fully supportive of the president. Sanders called for an end to establishment politics and the beginning of radical change. Clinton appealed to the head, Sanders to the heart.

The division was best exposed on health care, which has become the marquee issue in the primary. Sanders, who unveiled the long-awaited details of his single-payer health care plan just two hours before the debate, spoke in the language of rights and morality.

Clinton, meanwhile, spoke in the language of feasibility, suggesting Sanders’ plan would never work. And she warned following his approach would plunge the country back into a “contentious debate on health care,” having survived one of her own in the 1990s and witnessed the fight to enact the Affordable Care Act in 2009.

The candidates clashed again on Wall Street reform, with Sanders deploying a new attack on Clinton by invoking Clinton’s paid speeches. “I don’t take money from big banks,” he said. “I don’t get personal speaking fees from Goldman Sachs.”

Clinton did land a few blows with well-deployed opposition research, ticking off a litany of Sanders’ pro-gun votes at a time where Obama and many progressive voters are calling for stricter gun safety measures. And she challenged Sanders on his Wall Street attacks by unexpectedly invoking Sanders’ vote for the Commodity Futures Modernization Act, which exempted “over the counter” derivatives from regulation.

Sanders mostly let the attacks roll off his back, but he did call the Clinton campaign’s claims about his gun record “very disingenuous” without providing details (fact checkers have sided with Clinton.)

Obama is a personal issue here in South Carolina, where black voters dominate the Democratic primary process and the president is extremely popular. South Carolina could be part of Clinton’s Southern firewall if Sanders wins either or both Iowa or New Hampshire, since Sanders so far has struggled to win much support among African-Americans.

Asked about his comment that Bill Clinton’s conduct with Monica Lewinsky was totally disgraceful and unacceptable,” Sanders nimbly turned the question around on the moderators. He blamed the media for distracting him from the issue-based campaign he wanted to run – even as he showed no reservation about saying that Clinton’s husband’s actions were “deplorable” as she stood just a few feet away.